Method of and apparatus for deairing slips



Oct. 25, 1949. J. A. BOWER METHOD OF AND APPARATUS FOR DEAIRING SLIPSFiled Feb. 23, 1945 Patented Oct. 25, 1949 OFFICE METHOD OF ANDAPPARATUS FOR DEAIRING SLIPS a- James A. Bower, Chester, W. Va assignorto The "Taylor, Smith & '1aylor Company, East Liverpool, Ohio, acorporation of West Virginia Application February 23 1945, Serial No.579,461 it Claims. (ill. 2522) The invention relates to improvements inthe treatment of slip to be used in the casting of ceramic articles inplaster-of-Paris molds or other molds of porous material, andparticularly to the de-airing of the slip while it is en route from thestorage tank to the molds.

Slip is prepared from clay, with various ingredients, and it has longbeen known that air, in considerable quantity, is embodied in the slipin the form of minute bubbles. The harmful efiect iii of the air in theslip on the finished product has also long been known, and variouseiforts have been made heretofore to remove the air and thereby improvethe product. However, as far as is known, no one has ever disclosedheretofore any method or apparatus similar to the present invention, inwhich the slip while passing from the storage tank to the casting moldsis spread in a shallow layer or pool, and while being gently stirred oragitated, beneath the surface, is sub- 20 jected to a vacuum to removethe air or other gases which rise tothe surface.

One of the objects of the invention is to provide a new and improvedmethod and apparatus by which there is a continuous operatioxrofde fiairing the slip, so that when the slip leaves the storage tank it flowsthrough the de-airing chamber to the plaster-of-Paris casting moldswithout any opportunity for the accumulationof air after leaving thede-airing chamber.

Another object of the invention is to improve the de-airing operation byspreading the liquid slip in a shallow pool or stream having anexpansive surface, so that the air bubbles or other gases will morereadily and rapidly rise to the surface subjected to the vacuum in thede-airing chamber.

Another object of the invention is to further improve the de-airingoperation by gently stirring the shallow stream or pool of liquid slip,beneath the surface thereof, to thereby drive the bubbles to the surfaceand to prevent the formation of scum on the surface.

A further object of the invention is to prevent 2 operating, which isaccomplished by extending the discharge pipe upwardly to a point at ahigher level than the gravity head less the suction head.

Various other objects of the invention will be apparent to those skilledin the art, from the following detailed description in connection withthe accompanying drawings, in which Figure 1 is an elevational view ofthe apparatus, with parts broken away, and

Figure 2 is a vertical sectional View of the deairing or vacuum chamber,taken on line 2-2 of Figure 1.

The slip is prepared in the usual manner and after treatment in theblunger it is screened and then delivered to the upper end of anordinary storage tank 5, as by a pipe 2. This tank, which is usuallylarge enough to hold several days supply of slip, is shown in thedrawing as broken away at the center so that it can be of any desiredsize. The tank is preferably provided with the usual agitating elements3 carried by a shaft 6 which is connected by bevel gears 5 to a motor 6,

by which the shaft is continuously rotated, as is well kgo wnintheart.------- In accordance with the present invention the de-airing ofthe slip is a continuous operation; the liquid slip in the storage tankbeing delivered continuously to a 'de-airing or.vacuumgqhamber M throughwhich'it flows while being gently stirred or agitated, and beingcontinuously delivered from the de-airing chamber to plaster-of-Parismolds or other molds of porous material.

In the form illustrated, a pump 1, operated by a motor 8, draws the slipfrom the bottom of the storage tank I through a pipe 9 and delivers itthrough a pipe I to the bottom of a de-airing or vacuum chamber ll,preferably at a point adjacent one end thereof. The chamber is supportedin an elevated position on a frame l2.

This de-airing chamber is air-tight throughout 1 and may beof anydesirable shape, but in the particular form shown it is of considerablelength and thus there is presented an expansive surthe liquid Slip, inits flow from the de airmg face of the slip, so that there will be ampletime chamber to the porous casting molds, from becoming exposed to air.

Still another object of the invention is to prevent any entrapment ofair in the de-aired slip to de-air the slip as it flows from theentrance end of the chamber to the discharge end thereof.

The slip is continuously delivered to one end of the tie-airing chamber,and continuouslydisby keeping the pump which delivers the liquid slipcharged from e Opposi e e d ereof to t e to the molds, under a pressurehead of slip, so that the pump is filled and under pressure even whenthe pump is not operating.

Another object of the invention is to prevent casting molds, aspreviously mentioned, and in accordance with the present invention it isvery desirable that the pool or stream of liquid slip be rather shallow,so that it can be more quickly any dischar e of the slip when the pumpis not as and more thoroughly de-aired. Of course, the

invention is in no manner limited toany particular depth, and it may bevaried within wide limits in different circumstances, but a good depthis around one and one-half inches.

If the slip should be delivered to the molds I in less volumethan it isdelivered to the de-' airing chamber the slip would rise vinthe chamber,so that the pool or stream might reach a greater depth than desirable.-'In order to maintain a shallow stream at asubstantially constant level,means preferably is provided for temporarily stopping the pump 8 if thesurface of the slip rises above a desired level. For this purpose thechamber is preferably provided with a float member 13 so arranged thatif the slip rises above a desired level it will open a switch It andthereby stop the motor 8 which drives the pump 1. Of course, the pumpingoperation will be resumed as soon as the slip falls to the desired leveland the float thereby causes the switch to be closed.

Float controlled switches are so well known that a detailed illustrationand description are unnecessary.

The slip de-airing chamber is maintained at the desired degree of vacuumby any preferred means, and numeral refers to a vacuum line having oneend connected to the de-airing chamber and the other end leading to avacuum pump (not shown) or to any other desired source of vacuum. Thede-airing chamber is also preferably provided with a number of peepholes l6, so that the condition of the slip in the chamber can bereadily determined.

In accordance with the method and apparatus disclosed herein, it isdesirable to gently stir or agitate the slip, beneath the surface, inits course from the receiving end to the discharge end of the de-airingchamber, as previously mentioned. Of course, various means may beemployed for this purpose, but in the form illustrated, hollow columnsII project upwardly from the opposite ends of the de-airing chamber H,and as these columns communicate with the interior of the chamber theyare constantly under vacuum. A shaft l8 ismounted for oscillation in theupper'ends of these columns, and air-tight bushings l9 are provided toprevent leakage of air into the chamber. The shaft 18 is constantlyoscillated by any desired means. 'In the form shown; a crank arm 20 isattached to the end of shaft l8, and a connecting rod 2| has one endconnected to the crank arm and the other end eccentrically connected toa disc 22 which is continuously rotated by a motor 23 through speedreduction gearing 24.

The shaft [8 carries depending arms 25 which are attached at their lowerends to a stirring or agitating member 26, which is shown in the form ofa bar, but may be of any desired form.

The arc of swing of the agitating member is preferably such that italways remains under the Y surface of the slip, as shown in Figure 2.The movement of the agitating member .back and forth gently stirs theslip as it travels from one end of the chamber to the other, so that theair bubbles rise to the surface. In accordance with the inventionthereis an expansive surface, and the stream or pool is shallow, so that theslip is thoroughly and rapidly de-aired before it reaches the dischargeend of the chamber. And as the agitating member is moving back and forthonly a short distance below the slip surface, its action is such that italso performs the very important function of preventing the accumulationof scum on the surface.

The tie-aired slip ishow ready for delivery to .the casting molds, and,of course, it is important thatno air bubbles be picked up by the slipin its passage to the molds. The preferred means by -which the slip isdelivered from the tie-airing chamber to the casting molds, withoutexposure diaphragm pump 28. Another pipe 29 leads from.

. the discharge side of the pump to any desired means for introducingthe slip into the plasterof-Paris molds.

As diaphragm pumps are wellknown, it is unnecessary to illustrate ordescribe the pump in detail; it being sufficient to point out that checkvalves 30 and 3| are provided at the inlet and discharge ends,respectively, and a pipe 32 leads from a source of air pressure tooperate the diaphragm. A shut-off valve 33-may be provided in the pipe21.

By reference to Figure 1 it will be noted that the de-airing chamber IIis above the pump 28. The vertical distance between the chamber and thepump is such that the pump is always under a pressure head. In otherwords, there is a vacuum head in the pipe 21, due to the vacuum in thede-airing chamber, and for the purpose of illustration it is assumedthat the vacuum head extends down to thehorizontal dash line shown inthe lower left hand corner of Figure 1. Now by locating the pump belowthe vacuum head, i. e.', below the dash line of Figure 1, there isalways a pressure head on the pump, with the result that the pump isalways full of slip and always under pressure, even when the pump is notoperating. Thus it is apparent that no air will be entrapped in the pumpto possibly contaminate the de-aired slip.

It is also desirable that there be no flow of the slip to the castingmolds when the pump is not operating. For this purpose the pipe 29 fromthe delivery side of the pump extends upwardly a short distance abovethe dash line representing the vacuum head in Figure 1. That is, thepipe 29 extendsto a point higher than the gravity head less the vacuumhead, and hence the slip will flow through the pump 28 and pipe 29 upto, but not beyond, the dash line representing the vacuum head, so thatno slip will be discharged from the pipe 29 unless the pump isoperating.

It should also be mentioned that the present invention is also useful inhand delivery, for means can be provided for drawing off the slip asdesired at any point in the discharge line from the de-airing chamber,where the gravity head is greater than the vacuum head.

It is thought that the manner in which the method is carried out, andthe operation of the apparatus, will be clearly understood from theforegoing description, but a brief summary may be desirable. Theprepared slip is delivered to the storage tank which is preferably ofsuificient size to hold several days supply, and while in the tank theslip is preferably agitated by continuously rotating elements 3.

The slip is pumped from the storage tank to 'the de-airing chamber,which is under constant vacuum, and at the same time slip is withdrawnfrom the de-airing chamber for delivery to the casting molds, so thatthe process is a continuous one; the slip being de-aired whileit is onits way to the molds. The slip is preferably maintained in a shallowpool or stream in its flow from the entrance end to the discharge end ofthe de-airing chamber, so that the air bubbles will more easily reachthe surface. In order to maintain the slip at the desired shallow depth,in-case the slip is not drawn oil as fast as it is delivered to thechamber, there is preferably provided a float-controlled switch totemporarily stop the pump 8.

While the slip is flowing from the entrance end to the discharge end ofthe tie-airing chamber it is gently agitated or stirred to cause the airbubbles to rise to the surface, and this stirring operation ispreferably entirely below the surface of the flowing stream, whereby theaccumulation of scum on the surface is prevented.

This method of continuously de-airing the slip in its passage to themolds is very eilicient and very rapid, and while the invention is in nomanner limited to any particular means for stirring the slip while inthe chamber, or to any particular form of chamber, yet I prefer one ofoblong shape. The length of the chamber may vary greatly in differentinstallations, depending upon various factors, but in ordinarycircumstances a length in the neighborhood of twelve feet is more thanample to assure complete de-airing. It will at once be apparent to thoseskilled in the. art, that with such an expansive surface under vacuumand with a shallow stream being constantly stirred, the de-airingprocess will be performed with great rapidity and thoroughness.

The de-aired slip is constantly withdrawn from the chamber and deliveredto the casting molds, preferably by pump. This pump is located 'at avertical distance below the chamber greater than the vacuum head, sothat the pump is always filled and under a pressure head, even when thepump is not operating, and hence there is no chance of entrapment ofair. And, as previously mentioned, the delivery pipe from the pumppreferably extends upwardly a distance greater than the gravity headless the vacuum head, so that there will be no discharge of slip whenthe pump is not operating.

Having fully described the claim is:

1. Apparatus for de-airing slip including a vacuum chamber adapted tocontain liquid slip, a

pump for delivering the slip from the vacuum chamber to molds in whichthe slip is to be cast into ceramic articles, and said vacuum chamberbeing at a greater distance above the pump than the height of a columnof slip which the vacuum in the chamber will support, whereby the pumpis under a pressure head.

2. Apparatus for de-airing slip including a vacuum chamber adapted tocontain liquid slip, a pump for drawing slip from the vacuum chamber,

said vacuum chamber being at a greater distance above the pump than theheight of a column of slip which the vacuum in the chamber will support,whereby the pump is always under a pressure head, and a pipe fordelivering the slip from the discharge end of said pump to molds inwhich the slip is to be cast into ceramic articles, said pipe extendingupwardly to a point greater than the difference between the gravity headand the vacuum head of the slip, whereby there will be no discharge ofslip except when the pump is operating.

3. Apparatus for de-airing slip including a vacuum chamber, means fordelivering slip to the invention, what I 6 vacuum chamber, means forstirring the slip in the vacuum chamber, a pump for delivering slip fromthe vacuum chamber to molds in which the slip is to be cast into ceramicarticles, and said vacuum chamber being at a greater distance above thepump than the height of a column of slip which the vacuum in the chamberwill support, whereby the pump is under a pressure head.

4. In the casting of ceramic articles in molds, the method of de-airingthe liquid slip en route to the molds, which comprises continuouslyflowing a shallow stream of slip having an expansive surface through achamber, gently stirring the stream as it flows through the chamber, andsubjecting the expansive surface of the stream to vacuum during its flowthrough the chamber.

5. In the casting of ceramic articles in molds, the method of de-airingthe liquid slip en route to the molds, which comprises continuouslyflowing a shallow stream of slip having an expansive surface through achamber, gently stirring the tially horizontal stream below its surfaceas it flows through the chamber, and subjecting the expansive surface ofthe stream to vacuum during its flow through the chamber.

6. In the casting of ceramic articles in molds, the method of de-airingthe liquid slip en route to the molds, whichcomprises continuouslyflowing a shallow stream of slip having an expansive surface through achamber, gently stirring the stream close to but beneath the surfacethereof as it flows through the chamber, and subjecting the expansivesurface of the stream to vacuum during its flow through the chamber.

7. In the casting of ceramic articles in molds, the continuous method ofde-airing the liquid slip while passing from a storage tank to castingmolds, which comprises continuously flowing the liquid slip to achamber, continuously flowing the slip in a shallow stream having anexpansive surface through the chamber, gently stirring the stream as itflows through the chamber, subjecting the expansive surface of thestream to vacuum during its flow through the chamber, and continuouslyflowing the slip from the chamber to the casting molds withoutopportunity for the accumulation of air after leaving the de-airingchamber.

8. Apparatus for de-airing slip including a vacuum chamber, means forcontinuously flowing liquid slip through said chamber in a substantiallyhorizontal plane, means for continuously withdrawing de-aired slip fromthe vacuum chamber and delivering it to casting molds, and means forgently stirring the slip while in the chamber, said stirring means beinglocated within the slip and below the surface thereof.

v 9. Apparatus for de-airing slip including a vacuum chamber, means forcontinuously flowing liquid slip through said chamber in a substanplane,means for continuously withdrawing de-aired slip from the vacuum chamberand delivering it to casting molds, and means for gently stirring theslip while in the chamber, said stirring means positioned within theslip and close to but below the surface thereof.

10. Apparatus for de-airing slip including a vacuum chamber, means forcontinuously flowing liquid slip through said chamber in a substantiallyhorizontal plane, means for continuously withdrawing de-aired slip fromthe vacuum chamber and delivering it to casting molds, and means forgently stirring the slip while in the face of the liquid slip.

mamas? 7 chamber, said stirring means including an elongated rod-likemember and means for moving the rod-like member back and forth beneaththe sur- JAMESVA. BowER.

REFERENCES crmn The following 'eterences are of record in the ille ofthis patent:

Number 346,198

UNITED STATES PATENTS Name Date Fowler July 27, 1886 Bkidmore Jan. 1'1,1922 Lapp Aug. 8. 1922 Ross et al Dec. 11,1928 Curtis Mar. 5, 1929VanderHenst Jan. 3, 1939

